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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 87 of 326

This practice set contains high-yield board review questions covering key concepts in 3. Adult Reconstruction (Hip & Knee). Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1721

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old female presents with progressive groin pain 6 years after an uncomplicated metal-on-polyethylene total hip arthroplasty utilizing a modular titanium stem and a large-diameter cobalt-chromium head. Inflammatory markers are normal and an aspiration is negative for infection. MRI with MARS sequencing reveals a large, thick-walled cystic mass communicating with the joint. Serum ion levels show Cobalt is 8.5 ppb and Chromium is 1.1 ppb. What is the most likely pathophysiologic mechanism for her condition?

. Volumetric wear of the ultra-high molecular weight polyethylene liner
. Mechanically assisted crevice corrosion at the head-neck junction
. Type IV delayed hypersensitivity to the titanium femoral stem
. Galvanic corrosion at the stem-cement interface
. Aseptic loosening secondary to third-body wear

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck junction

Explanation

The patient is experiencing an adverse local tissue reaction (ALTR) secondary to trunnionosis, which is mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (the trunnion). In metal-on-polyethylene THA, significant elevations in serum cobalt with normal or minimally elevated chromium levels strongly suggest corrosion at the modular cobalt-chromium head and titanium stem taper junction. This is distinguished from metal-on-metal bearing wear, which typically presents with equally elevated cobalt and chromium levels.

Question 1722

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old female presents with an audible and palpable 'catch' in her knee 14 months after a primary posterior-stabilized total knee arthroplasty. The catching occurs consistently when the knee moves from 45 degrees of flexion to 30 degrees of flexion during active extension. Range of motion is 0 to 120 degrees. Radiographs show well-fixed components with no signs of loosening. What is the anatomic basis for this phenomenon?

. A loose body impinging in the lateral gutter
. A prominent popliteus tendon snapping over the lateral femoral condyle
. A fibrous nodule at the superior pole of the patella engaging the intercondylar box
. Impingement of the deep MCL against an overhanging tibial tray
. Asymmetric wear of the medial compartment of the polyethylene insert

Correct Answer & Explanation

. A fibrous nodule at the superior pole of the patella engaging the intercondylar box

Explanation

This is the classic presentation of 'patellar clunk syndrome', a complication historically associated with posterior-stabilized (PS) knee designs. It is caused by the formation of a fibrosynovial nodule on the undersurface of the quadriceps tendon just proximal to the superior pole of the patella. As the knee flexes, the nodule enters the intercondylar box of the femoral component. As the knee actively extends from roughly 45 to 30 degrees, the nodule abruptly pops out of the box, creating a painful clunk.

Question 1723

Topic: 3. Adult Reconstruction (Hip & Knee)

A 74-year-old female presents for revision total hip arthroplasty due to severe aseptic loosening of her acetabular component. Preoperative radiographs demonstrate more than 3 cm of superomedial migration of the cup. The teardrop is completely obliterated, and Kohler's line is crossed, indicating extensive medial wall destruction. Based on the Paprosky classification of acetabular defects, what is her defect type?

. Type 2A
. Type 2B
. Type 3A
. Type 3B
. Pelvic Discontinuity

Correct Answer & Explanation

. Type 3B

Explanation

The patient has a Paprosky Type 3B defect. This is characterized by severe bone loss with 'up and in' migration of the acetabular component. Key radiographic findings include >3 cm of superior migration, medial migration crossing Kohler's line, and obliteration of the radiographic teardrop. Type 3A defects show 'up and out' migration (>3 cm superolateral migration) with intact medial wall (Kohler's line not crossed).

Question 1724

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 Musculoskeletal Infection Society (MSIS) / International Consensus Meeting (ICM) criteria, which of the following sets of synovial fluid laboratory values is the threshold for diagnosing a chronic periprosthetic joint infection in a total knee arthroplasty?

. WBC > 1,500 cells/µL and PMN > 65%
. WBC > 3,000 cells/µL and PMN > 80%
. WBC > 10,000 cells/µL and PMN > 90%
. WBC > 25,000 cells/µL and PMN > 95%
. WBC > 50,000 cells/µL and PMN > 75%

Correct Answer & Explanation

. WBC > 3,000 cells/µL and PMN > 80%

Explanation

Based on the 2018 ICM criteria for diagnosing PJI, the established threshold for synovial fluid in chronic periprosthetic joint infections of the hip and knee is a WBC count > 3,000 cells/µL or a polymorphonuclear (PMN) percentage > 80%. Acute infections (typically defined as within the first 6 weeks postoperatively) have higher thresholds, classically WBC > 10,000 cells/µL and PMN > 90%.

Question 1725

Topic: 3. Adult Reconstruction (Hip & Knee)

A 42-year-old male undergoes a primary THA using a ceramic-on-ceramic bearing. One year postoperatively, he complains of a loud, high-pitched squeaking noise coming from his hip when he walks, bend over, or performs deep squats. He denies pain. Radiographs demonstrate the acetabular cup is positioned in 60 degrees of inclination and 35 degrees of anteversion. What is the primary tribological mechanism leading to squeaking in this scenario?

. Galvanic corrosion at the trunnion
. Third-body wear from residual bone cement
. Edge loading leading to disruption of fluid-film lubrication
. Impaction of the ceramic head against a prominent anterior inferior iliac spine
. Phase transformation of the zirconia-toughened alumina

Correct Answer & Explanation

. Edge loading leading to disruption of fluid-film lubrication

Explanation

Squeaking is a specific complication of ceramic-on-ceramic (CoC) bearings, occurring in up to 1-10% of patients. The most common cause is edge loading, which often results from component malposition (such as excessive inclination > 50 degrees or abnormal anteversion). Edge loading leads to stripe wear and the loss of the thin fluid-film lubrication layer between the bearing surfaces. This localized dry friction creates high-frequency vibrations perceived as a squeak.

Question 1726

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female experiences a catastrophic disruption of her patellar tendon 3 months following a revision total knee arthroplasty. Primary repair is deemed impossible due to poor tissue quality. The surgeon plans an extensor mechanism reconstruction using a synthetic mesh (e.g., Marlex mesh). During the procedure, what is the critical step regarding the positioning of the knee when tensioning and securing the mesh to ensure clinical success?

. The mesh should be tensioned tightly with the knee in 90 degrees of flexion
. The mesh should be tensioned tightly with the knee in 30 degrees of flexion
. The mesh should be tensioned tightly with the knee in full (0 degrees) extension
. The mesh should be secured loosely in full extension to allow for postoperative stretching
. The mesh should be tensioned with the knee in 120 degrees of flexion to maximize range of motion

Correct Answer & Explanation

. The mesh should be tensioned tightly with the knee in 90 degrees of flexion

Explanation

When performing an extensor mechanism reconstruction using synthetic (Marlex) mesh or an allograft, it is paramount that the construct is tensioned maximally with the knee in full extension (0 degrees). Postoperatively, these constructs invariably stretch out. If tensioned in flexion or secured loosely, the patient will develop an immediate extensor lag that progressively worsens, leading to clinical failure. Postoperative protocol typically involves rigid immobilization in full extension for 6 to 8 weeks.

Question 1727

Topic: 3. Adult Reconstruction (Hip & Knee)

Understanding normal native knee kinematics is essential for optimizing total knee arthroplasty design. During normal active knee flexion from 0 degrees to 120 degrees, which of the following describes the characteristic motion of the tibiofemoral contact points in the axial plane?

. Both medial and lateral condyles translate anteriorly by an equal amount
. Both medial and lateral condyles translate posteriorly by an equal amount
. The medial condyle rolls back substantially while the lateral condyle remains stationary
. The medial condyle acts as a ball-in-socket with minimal translation, while the lateral condyle rolls back posteriorly
. The lateral condyle translates anteriorly while the medial condyle rolls back posteriorly

Correct Answer & Explanation

. Both medial and lateral condyles translate anteriorly by an equal amount

Explanation

Normal knee kinematics are characterized by 'medial pivot' motion. During flexion, the medial femoral condyle acts largely like a ball-in-socket joint with minimal anterior-posterior translation. In contrast, the lateral femoral condyle demonstrates significant posterior rollback. This asymmetric rollback results in internal rotation of the tibia relative to the femur during flexion (and the opposite, external rotation during terminal extension, known as the 'screw-home mechanism'). Medial pivot TKA designs attempt to replicate this specific kinematic pattern.

Question 1728

Topic: 3. Adult Reconstruction (Hip & Knee)

An 82-year-old female sustains a mechanical fall 8 years following a primary cementless total hip arthroplasty.

Radiographs reveal a periprosthetic femur fracture that originates at the tip of the stem and extends proximally. The stem is visibly loose, migrating distally by 1 cm. The proximal femoral bone stock demonstrates substantial osteolysis but the diaphyseal bone distal to the fracture is robust. According to the Vancouver classification, what is the type of fracture and the most appropriate definitive management?

. Vancouver B1; treated with open reduction and internal fixation utilizing locking plates and cables
. Vancouver B2; treated with revision THA using a long, fully porous or fluted tapered diaphyseal-engaging stem bypassing the fracture
. Vancouver B3; treated with proximal femoral replacement (tumor prosthesis)
. Vancouver C; treated with open reduction and internal fixation
. Vancouver A; treated with conservative management and protected weight-bearing

Correct Answer & Explanation

. Vancouver B1; treated with open reduction and internal fixation utilizing locking plates and cables

Explanation

This is a Vancouver B2 periprosthetic femur fracture. The fracture occurs around or just below the stem tip (Type B), the stem is loose (distinguishes B2/B3 from B1), and there is adequate bone stock distal to the fracture to support fixation (distinguishes B2 from B3). The standard of care for a Vancouver B2 fracture is revision of the femoral component using a long cementless stem (often fluted and tapered) that achieves secure diaphyseal fixation at least 2 cortical diameters distal to the most distal fracture line. B1 fractures have a well-fixed stem and are treated with ORIF. B3 fractures have severe bone loss requiring proximal femoral replacement or allograft-prosthetic composites.

Question 1729

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female requires a primary total knee arthroplasty for end-stage osteoarthritis. During her preoperative evaluation, she reports a severe, blistering skin reaction to cheap jewelry and watch bands. She believes she has a 'metal allergy'. According to the American Academy of Orthopaedic Surgeons (AAOS) guidelines, what is the most appropriate management regarding component selection?

. Perform standard preoperative patch testing; if positive, delay surgery indefinitely
. Order a Lymphocyte Transformation Test (LTT); proceed with standard cobalt-chromium implants if negative
. Proceed with standard cobalt-chromium implants, as dermal hypersensitivity does not correlate with deep joint allergy
. Utilize an oxidized zirconium or titanium femoral component and all-polyethylene or titanium tibial tray to avoid nickel exposure
. Administer a prophylactic course of systemic corticosteroids and use standard implants

Correct Answer & Explanation

. Perform standard preoperative patch testing; if positive, delay surgery indefinitely

Explanation

While the true incidence and clinical impact of metal hypersensitivity (Type IV delayed hypersensitivity) in total joint arthroplasty remain controversial, current consensus recommends that patients with a compelling history of severe metal allergy (e.g., severe blistering from jewelry, known nickel allergy) should receive hypoallergenic implants. Standard cobalt-chromium alloys contain small amounts of nickel. Options to avoid nickel include oxidized zirconium (Oxinium) femoral components, titanium alloy components, or entirely all-polyethylene tibial components.

Question 1730

Topic: 3. Adult Reconstruction (Hip & Knee)

A dual mobility cup is utilized in a 71-year-old male undergoing revision total hip arthroplasty for recurrent instability. Three years later, he presents with acute hip pain and shortening of the limb after a minor twisting injury. Radiographs show eccentric seating of the metallic femoral head within the acetabular cup, creating a 'bubble sign', but the large polyethylene bearing remains contained within the metal acetabular shell. What is the most specific complication unique to dual mobility bearings that has occurred?

. Extra-articular dislocation of the large polyethylene liner
. Intra-prosthetic dislocation due to wear or failure of the poly liner's retentive rim
. Aseptic loosening of the cementless metallic shell
. Dissociation of the modular titanium neck
. Galvanic corrosion of the inner metallic head

Correct Answer & Explanation

. Extra-articular dislocation of the large polyethylene liner

Explanation

Intra-prosthetic dislocation (IPD) is a complication unique to dual mobility (DM) articulations. It occurs when the inner small metallic femoral head dislocates out of the larger mobile polyethylene liner. This typically happens as a late complication due to wear of the retentive rim of the polyethylene liner, or acutely due to improper assembly or impingement. Radiographically, the 'bubble sign' is classic: the small metal head is eccentrically positioned within the outer metal cup, indicating it has escaped the polyethylene liner which is radiolucent.

Question 1731

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon assesses the gaps and finds the knee is well-balanced in extension but unacceptably tight in flexion. Which of the following intraoperative modifications will best address this imbalance without altering the extension gap?

. Resect additional distal femur
. Upsize the femoral component
. Downsize the femoral component using anterior referencing
. Release the posterior capsule
. Recut the proximal tibia with a decreased posterior slope

Correct Answer & Explanation

. Resect additional distal femur

Explanation

Downsizing the femoral component while using an anterior referencing system translates the posterior condyles anteriorly, thereby increasing the flexion gap. This maneuver does not affect the distal femoral resection, keeping the extension gap unchanged.

Question 1732

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents 8 years post-total hip arthroplasty (metal-on-polyethylene bearing with a 36-mm cobalt-chrome head) with new-onset groin pain. Serum inflammatory markers are normal. MRI with metal artifact reduction shows a solid cystic mass adjacent to the hip joint. Joint aspiration yields cloudy fluid with a negative culture. What is the most likely diagnosis?

. Periprosthetic joint infection (PJI)
. Trunnionosis with adverse local tissue reaction (ALTR)
. Polyethylene wear-induced osteolysis
. Iliopsoas impingement
. Aseptic component loosening

Correct Answer & Explanation

. Periprosthetic joint infection (PJI)

Explanation

Large cobalt-chrome heads on titanium stems increase torque and micromotion at the head-neck junction. This can lead to mechanically assisted crevice corrosion (trunnionosis) and subsequent ALTR, presenting as a sterile, cystic pseudotumor.

Question 1733

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary posterior-stabilized total knee arthroplasty, the surgeon checks the gap kinematics with trial components. The extension gap is perfectly balanced, but the flexion gap is excessively tight. Which of the following is the most appropriate surgical step to achieve a balanced knee?

. Recut the proximal tibia with more slope
. Release the posterior capsule
. Downsize the femoral component
. Upsize the femoral component
. Perform a medial epicondylar osteotomy

Correct Answer & Explanation

. Recut the proximal tibia with more slope

Explanation

A tight flexion gap with a balanced extension gap requires altering the femoral side in flexion. Downsizing the femoral component increases the flexion gap without affecting the extension gap.

Question 1734

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female presents with an inability to actively extend her knee 3 weeks after a primary total knee arthroplasty. Imaging reveals well-fixed components and a complete mid-substance patellar tendon rupture. What is the most reliable surgical treatment?

. Primary end-to-end repair with heavy non-absorbable sutures
. Primary repair augmented with cerclage wire
. Extensor mechanism allograft reconstruction
. Revision to a hinged total knee arthroplasty
. Gastrocnemius rotational flap

Correct Answer & Explanation

. Primary end-to-end repair with heavy non-absorbable sutures

Explanation

Primary repair of a disrupted extensor mechanism after TKA has an unacceptably high failure rate. Extensor mechanism allograft reconstruction with rigid fixation is the most reliable treatment for complete tendon ruptures with well-fixed components.

Question 1735

Topic: 3. Adult Reconstruction (Hip & Knee)

A 75-year-old male sustains a fall 5 years after receiving a primary cementless total hip arthroplasty. Radiographs demonstrate a displaced spiral fracture around the distal tip of the femoral stem. The stem has subsided 15 mm and appears loose. What is the Vancouver classification and appropriate management?

. Vancouver B1; Open reduction and internal fixation with a locking plate and cables
. Vancouver B2; Revision to a fully porous-coated long stem or fluted tapered modular stem
. Vancouver B3; Proximal femoral replacement
. Vancouver C; Open reduction and internal fixation with cortical allograft struts
. Vancouver A; Nonoperative management with protected weight-bearing

Correct Answer & Explanation

. Vancouver B1; Open reduction and internal fixation with a locking plate and cables

Explanation

A fracture around a loose stem with adequate bone stock is a Vancouver B2 fracture. The standard of care is revision arthroplasty using a long uncemented stem (often fluted and tapered) that bypasses the fracture by at least 2 cortical diameters.

Question 1736

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain. Radiographs show well-fixed components with no osteolysis. Serum cobalt levels are significantly elevated, while chromium levels are normal. An MRI with metal artifact reduction shows a cystic pseudotumor. What is the most likely diagnosis?

. Polyethylene wear-induced osteolysis
. Adverse local tissue reaction (ALTR) secondary to trunnionosis
. Chronic periprosthetic joint infection
. Iliopsoas impingement
. Galvanic corrosion at the acetabular shell-screw interface

Correct Answer & Explanation

. Polyethylene wear-induced osteolysis

Explanation

Elevated cobalt levels disproportionate to chromium in a metal-on-polyethylene bearing strongly indicate mechanically assisted crevice corrosion (trunnionosis) at the head-neck taper. This leads to an adverse local tissue reaction (ALTR) or pseudotumor formation.

Question 1737

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered an absolute major criterion for the diagnosis of periprosthetic joint infection (PJI)?

. Serum CRP > 10 mg/L
. Synovial fluid leukocyte count > 3000 cells/uL
. A sinus tract communicating with the joint
. A single positive intraoperative culture
. Positive alpha-defensin test

Correct Answer & Explanation

. Serum CRP > 10 mg/L

Explanation

According to the 2018 ICM criteria, the two major criteria for diagnosing PJI are a sinus tract communicating with the joint or two positive cultures of the same organism. Minor criteria include elevated synovial WBC, CRP, and positive alpha-defensin.

Question 1738

Topic: Total Hip Arthroplasty (THA)

A patient dislocates their total hip arthroplasty anteriorly during extension and external rotation. Which of the following component malpositions is most commonly associated with this specific direction of instability?

. Excessive retroversion of the acetabular component
. Excessive anteversion of the acetabular component
. Decreased femoral offset
. Varus positioning of the femoral stem
. Excessive posterior tilt of the pelvis

Correct Answer & Explanation

. Excessive retroversion of the acetabular component

Explanation

Anterior dislocation of a THA typically occurs with the hip in extension and external rotation. It is most commonly associated with excessive anteversion of the acetabular or femoral components.

Question 1739

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with an audible and palpable 'pop' in her knee when extending from a flexed position, 1 year after a posterior-stabilized total knee arthroplasty. What is the most likely etiology of this phenomenon?

. Impingement of the popliteus tendon on the femoral component
. A fibrotic nodule on the deep surface of the distal quadriceps tendon catching in the intercondylar notch
. Polyethylene wear of the tibial insert
. Aseptic loosening of the patellar button
. Oversized femoral component leading to soft tissue stretching

Correct Answer & Explanation

. Impingement of the popliteus tendon on the femoral component

Explanation

Patellar clunk syndrome occurs in posterior-stabilized TKA when a fibrotic nodule forms at the superior pole of the patella. It catches in the femoral intercondylar box during flexion and 'clunks' out during active extension (usually around 30-45 degrees).

Question 1740

Topic: 3. Adult Reconstruction (Hip & Knee)

Manufacturers often add Vitamin E to highly cross-linked polyethylene (HXLPE) liners used in total hip arthroplasty. What is the primary biomaterial purpose of this addition?

. To increase the ultimate tensile strength of the polymer
. To quench free radicals and prevent long-term oxidative degradation
. To reduce the coefficient of friction against the femoral head
. To increase the melting point to allow for high-temperature autoclaving
. To enhance osteointegration at the shell-liner interface

Correct Answer & Explanation

. To increase the ultimate tensile strength of the polymer

Explanation

Irradiating polyethylene to create cross-links generates free radicals, which can lead to oxidation and embrittlement. Vitamin E is an antioxidant doped into HXLPE to quench these free radicals without the need for post-irradiation melting.

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